When light passes through a color filter, some color components are removed. This is known as color subtraction. For example, a magenta filter would remove the green color, leaving the blue and red colors to transmit. General color filters take advantages of the absorption of pigment and dye molecules (color gel/lighting gel/gel) (see examples in FIG. 1) or the reflection of multi-layer thin films (dichroic filters). The former needs thick substrate to produce desired color effect but then causes low transmission (typically <40%), while the latter requires precision multi-layer deposition that can be time consuming in fabrication. Examples of the current technologies are:                Color gel (i.e. color filter/lighting gel/gel)absorption+transmission        Dichroic filter (i.e. thin-film filter/interference filter)reflection+transmission        Neutral density filter (i.e. ND filter)reduce the intensity of overall spectrum.        
By exploiting surface plasmon resonance (SPR), color subtraction can be achieved producing similar color effect and the corresponding fabrication process is relatively simple. Noble metal nanoparticles (NPs) have been shown to induce various colors depending on their shape, size, distribution and surrounding medium. The perceived color is generated from the absorption characteristics of the noble metal itself (intrinsic properties) and also the scattering arisen from the dimension and geometry of the NPs. However using single metal NP can only produce color tuning by varying its dimension. Hence, the tuning range is somewhat limited.
To overcome the shortcomings of the conventional noble metal NPs, a new material for color filter with a wider range of transmission and color tunability, and the related production method for the same are urgently needed.